Reinforcing beams of the type herein contemplated are well known in the art. A typical commercially used beam is constructed of a piece of roll formed channel or flanged channel structure having separate end sections suitably fixed to opposite ends thereof. The fabricated structure is made of untempered steel and, after fabrication, the resultant beam structure is tempered in ovens to give it ultrahigh strength characteristics.
The requirement to separately fabricate at least three separate components and to then assemble the components materially contributes to the costs involved in producing the composite tempered beam. Another cost contributor is the need to heat temper the beams after fabrication.
There have been proposals in the patented literature to provide a beam with a one-piece construction. Examples are included in the disclosures of the following patents: U.S. Pat. No. 4,919,473 and Japanese Patent Publication No. 8-258569. The approach apparently taken in these designs is to achieve adequate strength by forming the beam with a steel having a strength something less than ultrahigh strength steel and compensating for the lesser material strength by constructing the beam with a special impact resistant cross-sectional configuration. Others have proposed utter simplicity in cross-sectional configuration and have provided the required strength by initially forming a composite laminar sheet. See, for example, U.S. Pat. No. 5,272,341.
The present invention is based upon gaining the necessary strength by utilizing ultrahigh strength steel as a starting material rather than achieving the desired strength after formation by heat tempering. Heat treating sheet steel while it is still in a roll or coil formation is more economical than heat treating individually fabricated structures even though the heat process is made as nearly "continuous" as possible.
The problem presented by utilizing ultrahigh strength steel as a starting material is that it is not easily cold formed into three dimensional configurations. Simple stamping operations often result in the creation of internal stresses which can distort portions of the formed sheet metal especially flat sections. There is a need to provide a reinforcing beam of the type discussed which can overcome the problems noted above.